1. Field of the Invention
The present invention relates to a method of compressing letters, and more particularly to a method of compressing letters in a caller identification code system.
2. Description of the Prior Art
Due to market demands, telephone sets having caller identification code systems are becoming increasingly popular. A caller identification code generally includes the name or code of the caller, the time, the date, etc. When a call is coming in, the user may know in advance who is calling so that he/she may decide whether or not to answer the call. Such caller identification code systems certainly have positive effects.
Since the number of letters of the name of a person is generally within sixteen, and since ASCII utilizes codes of 8 bits for compiling codes representing 256 different signs in which the capital letters of the English alphabet are from 21H to 3AH of the hexadecimal number system, the memory unit for storing names included in the caller identification code systems are designed to be 16 bytes, which, however, requires improvement.
Referring to FIG. 1, in a telephone set having a caller identification code system, the data structure of the conventional caller identification code system is divided into three parts. The first part, referenced by the numeral 11, contains two bytes and is sued for storing time data. For instance, if a call comes at 10:30, then the time data stored will be "1030". The second part 12 also contains 2 bytes and is used to store date data. For instance, if it is November 20, then the data stored will be "1120". The third part 13 contains 16 bytes and is used to store the name codes of callers. For instance, if the name of the caller is "AB . . . N", then the data stored will be 21, 22,2E of the hexadecimal number system. The first and second parts employ the BCD codes, whereas the third part adopts the ASCII codes.
As a matter fact, since there are only 26 letters in the English alphabet and the name codes may simply consist of capital letters, 5 bits will be enough for encoding. It is not necessary to use 8 bits. But the address of memories generally has bytes as their units. In order to save memory space, every 5 bits is a unit. Storing five-digit-encoded data "one be one" in a memory whose unit of address is 8 bits (equivalent to 1 byte) makes it very complicated in data reading and writing as well as data processing.